The present disclosure relates to a device comprising a battery having a multiplicity of battery cells and a sensor system for the redundant determination of a battery current flowing through the poles of the battery. Furthermore, the disclosure relates to a method for the redundant determination of the battery current flowing through the poles of a battery.
Batteries are increasingly gaining significance as energy stores, especially for propulsion systems of vehicles. To determine the charging state of the batteries and also for safety reasons, the current flow in and out of the battery or also the current flow of the individual battery cells is measured. Since a defective current sensor endangers not only the correct operation of the vehicle drive but also represents a safety risk, it must be continuously monitored.
In many cases, a shunt is used for measuring current. Such shunt current sensors measure a voltage drop whereupon the current flowing through the shunt can be determined with the aid of Ohm's law. Since a large additional resistance is undesirable in the circuit, the resistance of the shunt is selected to be very much smaller than that of the load. Due to the small resistance, the voltage only drops slightly across it in consequence. This small voltage drop is amplified and evaluated by means of electronic circuits. In order to detect a defect of the shunt or of the measuring electronics and be able to respond to it, well thought-out monitoring strategies are needed.
Safety-related electrical and/or electronic systems in motor vehicles are subject to the ISO 26262 Standard. In this context, an Automotive Safety Integrity Level (ASIL) represents a safety requirement level, specified by ISO 26262, for safety-related systems in motor vehicles having the grades A to D. ASIL D designates the safety requirement stage having the highest requirements for safety.
For a sensor developed, e.g., according to ASIL C, imaging redundant or diversitary measuring paths is the state of the art. Measuring a diversitary measurement value, for example an electrical current, can be guaranteed, e.g., by using a second sensor of a different type of construction.
Such an arrangement is shown diagrammatically in FIG. 1. According to this, a current is measured by means of two mutually independent current sensors.
In this arrangement, a first current sensor 10 can be constructed as current sensor with a shunt. A measurement signal is evaluated in a current measuring ASIC 12 (application-specific integrated circuit). In addition, the first current sensor 10 comprises a separate diagnostic unit 14 which monitors the operability of the first current sensor 10 and a microcontroller 16 which conditions a first current measurement value IMS for output.
In contrast to the first current sensor 10, the second current sensor 20 is constructed as a current sensor with a Hall sensor. A measurement signal is again evaluated in a current measuring ASIC 22. In addition, the second current sensor 20 also comprises a separate diagnostic unit 24 which monitors the operability of the second current sensor 20 and a microcontroller 26 which conditions a second current measurement value IMH for output.
The current measurement value IMS of the first current sensor 10 and the current measurement value IMH of the second current sensor 20 are transferred to an evaluating unit 30. The evaluating unit 30 comprises a further microcontroller 32 which compares and qualifies the current measurement values IMS and IMH. The evaluating unit 30 delivers a qualified current output value IQ as output variable.
A further method is integrating comparators into the current sensor. In this arrangement, e.g., the voltage across the shunt is conducted into a measuring IC (integrated circuit), on the one hand, and on the other hand, the voltage is compared with a threshold voltage. If the threshold value is exceeded, the higher-level controller can evaluate a hardware signal and take measures.
DE 10 343 179 A1 describes a device for determining a current flow of a vehicle battery. As usual, the current is conducted into a fuse box and conducted there in parallel via a number of fuses. The voltage drops at the fuses are measured in order to determine the total current which can be considered with a battery status detector. The part-currents through individual fuses can be checked so that when a limit current is exceeded, a fault can be assumed.
DE 10 2011 080 703.2 describes a method for measuring electrical current. In this context, the current to be measured is divided to at least two paths arranged in parallel. Subsequently, the part-current flowing through each path is measured by a current sensor. In order to determine the total current, the two part-currents are added. To check the plausibility of the measured part-currents, a ratio of the two part-currents is formed. This ratio can be compared, e.g., with a ratio recorded in the definitely operative state and formed in the same way.